Daughter wants to leave home on the day she turns 18

Child has undergone psychiatric treatment. Refuses & not cooperate with it anymore. Engages in self harm. Spends a lot of time online activities. Influenced by lot of people unknown to us she acquainted through social media or online activities and with their support want to leave home and live independently with them. Receives good amount money from unknown sources/people parents have no knowledge about. Will not share any details of such people. Threatens parents to file complaints against them to child line or police with allegations of mental and physical abuse towards her, if she cant have her way. Threatens to sue parents if they don't hand over her legal identification documents. Dropped out of school on their own. threatens Parents to defame using social media etc. what legal recourse can parents take to protect her from becoming a victim if she leaves home. what legal recourse can parents take to know her online activities, intention of people helping her, providing her money etc. what legal recourse is available to ensure the parents are protected from such defamation or losses or injury sustained by others from her actions demanded by others. what legal process can be pursued to ensure her medical treatment can be resumed in light of several documents of prior treatments available.